1. Field of the Invention
This invention relates to a humidity sensor and manufacturing method thereof and, more particularly, to a humidity sensor capable of self-regulating temperature compensation and a manufacturing method thereof.
2. Description of the Prior Art
Many kinds of humidity sensors, including those with humidity sensitive ceramic elements, porous oxide humidity sensitive elements, MOS-type semiconductor elements and lithium chloride humidity sensitive elements have been proposed in the past. Among polymer humidity sensitive element field, a resistance type polymer humidity sensitive element is widely used as an electronic metering device, a humidifying/dehumidifying device, and a meteorological measurement device because resistance type polymer humidity sensitive elements have the characteristics of high precision, high stability and fast response speed.
Humidity is very difficult to accurately measure. A psychrometer humidity sensor or a hair hygrometer is unnecessary to modern technology. In the prior art, the output of a capacitive humidity sensor is independent of temperature variations. In contrast, a resistance type humidity sensor is dependent upon temperature and often produces large variations and errors in humidity measurement as a result. However, compared with the resistance type humidity sensor, the capacitive humidity sensor is expensive and the cost of the resulting circuit is high.
A humidity-sensitive element is a simple humidity sensor. The humidity-sensitive element employs a resistor and two kinds of capacitors. The humidity-sensitive element uses a film produced by a humidity-sensitive material to cover a substrate. The humidity-sensitive element uses a resistance rate and a resistance value variation to measure humidity when humid air contacts the film. There are many kinds of humidity-sensitive resistors, for example, a metal oxide humidity-sensitive resistor, a silicon humidity-sensitive resistor, and a ceramic humidity-sensitive resistor. The advantage of the humidity-sensitive resistor is that it is highly sensitive, however, it suffers the disadvantages of bad linearity and cannot be replaced once it is broken.
The linearity and clean air requirements of the humidity-sensitive element are very poor. The humidity-sensitive element is easily dirtied and the precision of its measurement functions thereby affected. Furthermore, the stability and the resistance curve are dependant upon temperature when exposed to external environments for a long time.